(1) Field of the Invention
The present invention relates to a control method of an internal combustion engine on the basis of an estimation value of an exhaust device temperature of the internal combustion engine.
(2) Description of the Related Art
In patent document 1 (JP-A-6-33810), there is disclosed a technique that a temperature of an exhaust gas is forecasted on the basis of various parameters indicating data of an engine and an operating state thereof, a temperature of an exhaust device is forecasted on the basis of the forecasted exhaust gas temperature and an information of an exhaust system part, and the exhaust gas temperature is controlled in a lowering direction, at a time when the forecasted exhaust device temperature is equal to or more than a predetermined allowable limit value. An exhaust gas temperature forecasting expression is created in accordance with a multi-variable analysis on the basis of the various parameters indicating the engine data and the operating state thereof. Further, a forecasting of a delay behavior of the exhaust device temperature from a change of the exhaust gas temperature is described by a statistical model having the exhaust gas temperature forecasting value as an input. In the statistical model mentioned above, a constant corresponding to a heat capacity or a heat resistance is determined in accordance with a parameter identification on the basis of an experimental result. In patent document 2 (JP-2008-51092), there is disclosed a technique that a temperature of an exhaust gas is indirectly detected on the basis of an internal resistance of an air fuel ratio sensor element, a delay time to a fuel increase is set in correspondence to a rate of change of the exhaust gas temperature at a time when the exhaust gas temperature reaches a predetermined temperature, and a fuel supply amount to an engine is increased after the delay time. In accordance with these techniques, it is possible to execute the fuel increase while taking into consideration a temperature rise delay behavior of the exhaust device to be protected, and it is possible to achieve a protection of the exhaust device while holding down a deterioration of a fuel consumption to a minimum.
However, in an internal combustion engine which is provided with a variable valve, an exhaust turbo supercharger, an idle stop mechanism, an exhaust catalyst early activation control function caused by an ignition timing phase lag, and the like, since there is a great number of affectors affecting the exhaust gas temperature, and the affector itself of the exhaust gas temperature changes complicatedly, the delay behavior of the exhaust device temperature is not uniquely defined with respect to the exhaust gas temperature. In the internal combustion engine mentioned above, if a transient behavior of the exhaust device temperature intends to be forecasted in accordance with the statistical model disclosed in the patent document 1, it is necessary to switch the constant corresponding to the heat capacity or the heat resistance sequentially in correspondence to the operating condition, and it is hard to secure a sufficient precision. Further, in the technique disclosed in the patent document 2, the exhaust gas temperature can be indirectly detected on the basis of the internal resistance of the air fuel ratio sensor element, however, with regard to the delay time from the detected exhaust gas temperature changing timing to the execution of the fuel increase while taking into consideration the transient delay of the exhaust device temperature, it is necessary to previously set its value in accordance with a matching or the like, and in the system in which a degree of freedom for operation is increased, there is such a problem that a great amount of man hour is necessary for the matching for setting the delay time.